J. H. Wolfe

Quantum-well states in copper thin films

A standard exercise in elementary quantum mechanics is to describe the properties of an electron confined in a potential well. The solutions of Schrödingers equation are electron standing waves—or ‘quantum-well’ states—characterized by the quantum number n, the number of half-wavelengths that span the well. Quantum-well states can be experimentally realized in a thin film, which confines the motion of the electrons in the direction normal to the film: for layered semiconductor quantum wells, the aforementioned quantization condition provides (with the inclusion of boundary phases) a good description of the quantum-well states. The presence of such states in layered metallic nanostructures isbelieved to underlie many intriguing phenomena, such as the oscillatory magnetic coupling of two ferromagnetic layers across anon-magnetic layer, and giant magnetoresistance. But our understanding of the properties of the quantum-well states in metallic structures is still limited. Here we report photoemission experiments that reveal the spatial variation of the quantum-well wavefunction within a thin copper film. Our results confirm an earlier proposal that the amplitude of electron waves confined in a metallic thin film is modulated by an envelope function (of longer wavelength), which plays a key role in determining the energetics of the quantum-well states.

Modification of the magnetic properties of Fe/Cr(001) by controlling the compensation of a vicinal Cr(001) surface

The degree of compensation of a normally uncompensated Cr(001) surface is controlled by using a curved substrate with steps parallel to the [100] direction. In this way, the degree of frustration caused by steps at the interface between an Fe overlayer and the Cr substrate can be systematically varied. Previous work on flat Cr(001) at temperatures below the Cr ordering temperature (311 K) has identified a critical Fe thickness of ∼35–38 A, below which the Fe films display a reduced remanence. For our curved Cr substrate, below this critical Fe thickness three phases are observed for low ( ∼5°) miscut angle respectively: (i) multidomain; (ii) single domain with magnetization perpendicular to the step edges; and (iii) single domain with magnetization parallel to the step edges. At the same temperature, for Fe films above the critical thickness, region (i) disappears and only regions (ii) and (iii) remain. In a second experiment, the adsorption of submonolayer Au on the Fe is ...